/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtIncompatible;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.Collection;
import java.util.Map;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Provides static methods for serializing collection classes.
 *
 * <p>This class assists the implementation of collection classes. Do not use this class to
 * serialize collections that are defined elsewhere.
 *
 * @author Jared Levy
 */
@GwtIncompatible
@ElementTypesAreNonnullByDefault
final class Serialization
{
    private Serialization()
    {
    }

    /**
     * Reads a count corresponding to a serialized map, multiset, or multimap. It returns the size of
     * a map serialized by {@link #writeMap(Map, ObjectOutputStream)}, the number of distinct elements
     * in a multiset serialized by {@link #writeMultiset(Multiset, ObjectOutputStream)}, or the number
     * of distinct keys in a multimap serialized by {@link #writeMultimap(Multimap,
     * ObjectOutputStream)}.
     */
    static int readCount(ObjectInputStream stream) throws IOException
    {
        return stream.readInt();
    }

    /**
     * Stores the contents of a map in an output stream, as part of serialization. It does not support
     * concurrent maps whose content may change while the method is running.
     *
     * <p>The serialized output consists of the number of entries, first key, first value, second key,
     * second value, and so on.
     */
    static <K extends @Nullable Object, V extends @Nullable Object> void writeMap(
            Map<K, V> map, ObjectOutputStream stream) throws IOException
    {
        stream.writeInt(map.size());
        for (Map.Entry<K, V> entry : map.entrySet())
        {
            stream.writeObject(entry.getKey());
            stream.writeObject(entry.getValue());
        }
    }

    /**
     * Populates a map by reading an input stream, as part of deserialization. See {@link #writeMap}
     * for the data format.
     */
    static <K extends @Nullable Object, V extends @Nullable Object> void populateMap(
            Map<K, V> map, ObjectInputStream stream) throws IOException, ClassNotFoundException
    {
        int size = stream.readInt();
        populateMap(map, stream, size);
    }

    /**
     * Populates a map by reading an input stream, as part of deserialization. See {@link #writeMap}
     * for the data format. The size is determined by a prior call to {@link #readCount}.
     */
    static <K extends @Nullable Object, V extends @Nullable Object> void populateMap(
            Map<K, V> map, ObjectInputStream stream, int size)
            throws IOException, ClassNotFoundException
    {
        for (int i = 0; i < size; i++)
        {
            @SuppressWarnings("unchecked") // reading data stored by writeMap
            K key = (K) stream.readObject();
            @SuppressWarnings("unchecked") // reading data stored by writeMap
            V value = (V) stream.readObject();
            map.put(key, value);
        }
    }

    /**
     * Stores the contents of a multiset in an output stream, as part of serialization. It does not
     * support concurrent multisets whose content may change while the method is running.
     *
     * <p>The serialized output consists of the number of distinct elements, the first element, its
     * count, the second element, its count, and so on.
     */
    static <E extends @Nullable Object> void writeMultiset(
            Multiset<E> multiset, ObjectOutputStream stream) throws IOException
    {
        int entryCount = multiset.entrySet().size();
        stream.writeInt(entryCount);
        for (Multiset.Entry<E> entry : multiset.entrySet())
        {
            stream.writeObject(entry.getElement());
            stream.writeInt(entry.getCount());
        }
    }

    /**
     * Populates a multiset by reading an input stream, as part of deserialization. See {@link
     * #writeMultiset} for the data format.
     */
    static <E extends @Nullable Object> void populateMultiset(
            Multiset<E> multiset, ObjectInputStream stream) throws IOException, ClassNotFoundException
    {
        int distinctElements = stream.readInt();
        populateMultiset(multiset, stream, distinctElements);
    }

    /**
     * Populates a multiset by reading an input stream, as part of deserialization. See {@link
     * #writeMultiset} for the data format. The number of distinct elements is determined by a prior
     * call to {@link #readCount}.
     */
    static <E extends @Nullable Object> void populateMultiset(
            Multiset<E> multiset, ObjectInputStream stream, int distinctElements)
            throws IOException, ClassNotFoundException
    {
        for (int i = 0; i < distinctElements; i++)
        {
            @SuppressWarnings("unchecked") // reading data stored by writeMultiset
            E element = (E) stream.readObject();
            int count = stream.readInt();
            multiset.add(element, count);
        }
    }

    /**
     * Stores the contents of a multimap in an output stream, as part of serialization. It does not
     * support concurrent multimaps whose content may change while the method is running. The {@link
     * Multimap#asMap} view determines the ordering in which data is written to the stream.
     *
     * <p>The serialized output consists of the number of distinct keys, and then for each distinct
     * key: the key, the number of values for that key, and the key's values.
     */
    static <K extends @Nullable Object, V extends @Nullable Object> void writeMultimap(
            Multimap<K, V> multimap, ObjectOutputStream stream) throws IOException
    {
        stream.writeInt(multimap.asMap().size());
        for (Map.Entry<K, Collection<V>> entry : multimap.asMap().entrySet())
        {
            stream.writeObject(entry.getKey());
            stream.writeInt(entry.getValue().size());
            for (V value : entry.getValue())
            {
                stream.writeObject(value);
            }
        }
    }

    /**
     * Populates a multimap by reading an input stream, as part of deserialization. See {@link
     * #writeMultimap} for the data format.
     */
    static <K extends @Nullable Object, V extends @Nullable Object> void populateMultimap(
            Multimap<K, V> multimap, ObjectInputStream stream)
            throws IOException, ClassNotFoundException
    {
        int distinctKeys = stream.readInt();
        populateMultimap(multimap, stream, distinctKeys);
    }

    /**
     * Populates a multimap by reading an input stream, as part of deserialization. See {@link
     * #writeMultimap} for the data format. The number of distinct keys is determined by a prior call
     * to {@link #readCount}.
     */
    static <K extends @Nullable Object, V extends @Nullable Object> void populateMultimap(
            Multimap<K, V> multimap, ObjectInputStream stream, int distinctKeys)
            throws IOException, ClassNotFoundException
    {
        for (int i = 0; i < distinctKeys; i++)
        {
            @SuppressWarnings("unchecked") // reading data stored by writeMultimap
            K key = (K) stream.readObject();
            Collection<V> values = multimap.get(key);
            int valueCount = stream.readInt();
            for (int j = 0; j < valueCount; j++)
            {
                @SuppressWarnings("unchecked") // reading data stored by writeMultimap
                V value = (V) stream.readObject();
                values.add(value);
            }
        }
    }

    // Secret sauce for setting final fields; don't make it public.
    static <T> FieldSetter<T> getFieldSetter(Class<T> clazz, String fieldName)
    {
        try
        {
            Field field = clazz.getDeclaredField(fieldName);
            return new FieldSetter<>(field);
        }
        catch (NoSuchFieldException e)
        {
            throw new AssertionError(e); // programmer error
        }
    }

    // Secret sauce for setting final fields; don't make it public.
    static final class FieldSetter<T>
    {
        private final Field field;

        private FieldSetter(Field field)
        {
            this.field = field;
            field.setAccessible(true);
        }

        void set(T instance, Object value)
        {
            try
            {
                field.set(instance, value);
            }
            catch (IllegalAccessException impossible)
            {
                throw new AssertionError(impossible);
            }
        }

        void set(T instance, int value)
        {
            try
            {
                field.set(instance, value);
            }
            catch (IllegalAccessException impossible)
            {
                throw new AssertionError(impossible);
            }
        }
    }
}
